Scale insects infesting papaya stem

I cannot seem to get rid of these lichen-like spots growing on my papaya plant. What are they and how can I remove them?

Jeff Poh

The white spots appear to be a type of scale insect, a sap-sucking pest. They are quite difficult to control at this stage, and early detection and management is often most effective.

Spray your plant with a commonly available pesticide, like summer oil or neem oil, and cover the infested portions thoroughly. These pesticides kill the pests via suffocation and are not toxic to beneficial predators.

You may want to rotate your pesticides for more effective control and to reduce the likelihood of the insects developing a pesticide resistance.

Maidenhair fern may need a new spot to thrive

My fern is turning brown at the leaf tips. How do I stop the browning and help my plant grow?

Ong Tin Si

The maidenhair fern can be difficult to grow as it cannot be allowed to dry out totally. Looking at the dry leaf tissues in the picture, it appears your fern has been dried out before.

This plant has very thin leaf tissues and is prone to drying out if it is not watered in a timely manner. If it is grown in a windy area, where water evaporates quickly, you should ensure you water it promptly.

The growing medium should be well-drained and moist, but not wet. Try using a timed irrigation device to dispense water at intervals if you cannot find time to water the plant.

Bauhinia may be suffering from salt damage; hydrangea needs nutrients

The leaves of my bauhinia and hydrangea plants are drying from the tips. The plants are fertilised every 10 days. What is wrong?

Sandra Tan

Has your bauhinia been growing in a small pot of soil for a long time? The frequent fertilising, especially with chemical fertiliser pellets, may have caused excess salts to accumulate in the root zone, leading to the blackening of the leaves.

You may want to stop the feeding and allow the salts to flush out from the soil via routine watering - a process that will take some time. Try moving the plant to a larger root space, so the roots do not dry out too quickly during the hot season.

As for your hydrangea, the nutrient deficiency appears to be quite advanced. It may be lacking essential mobile nutrients such as nitrogen and magnesium.

What kind of fertiliser are you using? Organic fertilisers, depending on the formulation, may not contain all the nutrients plants need for healthy growth. Ensure that the growing medium is not too compacted and wet. Check the soil pH level to ensure it is not too extreme, which can interfere with the plant's nutrient retention.

Aloe vera has fungal disease

My plant has depressed black spots on the leaves, even in areas of new growth. I place it in a spot which gets filtered sunlight and an hour of direct noon sun. I water it only when the top soil is dry, though it may sometimes be splashed with water from automatic sprinklers for nearby plants. What is wrong with my plant?

Chan Wing Seng

Aloe vera grown in the open in the tropics is prone to fungal leaf spots. Infected leaves will not recover and steps must be taken to prevent the future infection of new leaves.

Grow your plant under a clear shelter which protects it from rain during the wet season. Ensure it still gets direct sunlight and the root zone is well-drained. It should be allowed to dry out and not be constantly wet.

Fungicides, such as those based on antagonistic fungi like Trichoderma, can be applied to reduce the likelihood and severity of infection.

Plant appears to be an amaranthus species

What is this plant? Is it edible and how should I care for it?

Hsu Li Ren

The plant is likely an Amaranthus cultivar. It is a common leafy vegetable and is often called Chinese spinach and bayam in Singapore.

Your plant has started to flower and will die soon after, dispersing numerous black seeds. Leaves produced at this stage are likely to be old, tough and unpalatable.

You may want to collect the seeds and try growing them. Young plants produce more tender leaves. This plant grows best in fertile, well-drained soil, and in a spot which gets at least four hours of direct sunlight a day.

• Answers by Dr Wilson Wong, an NParks-certified practising horticulturist, parks manager and ISA-certified arborist. He is the founder of Green Culture Singapore and an adjunct assistant professor (Food Science & Technology) at the National University of Singapore.
• Have a gardening query? E-mail it with clear, high-resolution pictures of at least 1MB, if any, and your full name to stlife@sph.com.sg. We reserve the right to edit and reject questions.